The present invention generally relates to an apparatus useful with a chromatography column and, in particular, relates to an apparatus for maintaining a chromatography column at a uniform temperature.
In the general field of chromatography, it is well known that the successful analysis of a sample flowing through a chromatography column is often dependent upon the temperature of the column. The temperature of the column has a direct influence on almost all of the critical parameters of such an analysis. For example, in liquid chromatography; the viscosity of the solvent (and hence its fluidity and therefore its flow rate and back pressure); the retention of the sample by the stationary phase (and hence the clarity of sample component separation); the temperature gradient, if any, along the length of the column, such gradients are set up by what is commonly known as "heat of friction" and can easily be a significant influence, (and hence the reproducibility and uniform reliability of the separation); the temperature gradient, if any, across the cross-section of the column (and hence the uniformity of flow of the fluid front along the column upon which the distinctiveness of separation depends), as well as other critical parameters, are highly dependent upon the temperature of the column. Without a doubt, these are but a few of the factors taken into account during a chromatographic analysis, even when it is performed at, for example, room temperature. The magnitude of these difficulties is compounded when the analysis is performed at reduced or elevated temperatures.
Generally, insofar as liquid chromatography columns are concerned, the above-recited difficulties have been dealt with by use of either one of two means. In one prior art means, the column is located in a heated box, or oven. While this means reduces the effects of the difficulties, severe temperature gradients nonetheless exist and detrimentally influence the analysis. Such gradients exist primarily from the inability of conventional ovens to maintain uniform temperatures therein and thus such ovens require the continuous cycling of the heating element. Further, conventional ovens require the introduction of more heat than necessary to warm the surrounding air which is often cooler than the desired temperature. One major concern in this type of apparatus is the inherent time lag between the introduction of heat and the response of the temperature measuring means, e.g., a thermocouple. Further, because of the poor heat transfer between the oven air and the metal column, the top of the column is cooled rapidly by the influx of room temperature solvent. Consequently, a steep temperature gradient, as much as 15.degree. C., is created. Such a large temperature gradient inevitably reduces the separation efficiency of the column. As a consequence, the column within such an oven is not uniformly heated.
The other commonly used means is a generally heated column holder having a V-groove therein for generally positioning the column. Such an apparatus is unsatisfactory since the holder only contacts the column along two points of the V. Occasionally, a pair of these holders are used and thus the number of contact points becomes doubled. However, since the column is not uniformly contacted or secured, temperature gradients are formed both along the length of the column and across its cross-section.
Hence, it is highly desirable to provide an apparatus which substantially completely eliminates both axial and radial temperature gradients in a column during an analysis. The need is particularly great when an analysis is performed which requires the use of a guard column or a second column in series with a chromatography column.